Over the last two decades, the telecommunications industry has progressed from a copper based, low bandwidth network to a fiber optic based, high bandwidth network. Although this evolution is ongoing, there has been a significant investment in fiber optic plant which often lies adjacent copper based elements in the same network. As a result, testing devices used to monitor and evaluate communications lines are now required to accept both copper and fiber optic lines and protocols. The older T1, DS0, DS1, and DS3 formats used in copper plant feeds into the same nodes as OC-1, OC-3, OC-12, and OC-48 fiber optic modalities and these higher speed optical signals contain the lower order signals as embedded bit streams. It is therefore desirable to produce a test device that can fully extract, test and evaluate each of these formats within a single platform. It is further desirable to permit multiple tests of a single bit stream by routing signals from one signal modality to another through a high speed internal switch fabric. It is further desirable to produce a test device that can terminate and evaluate several high speed signals simultaneously. It is further desirable to produce a test device that can terminate and process very high speed signals without resort to expensive components.
Others have attempted to produce a fully integrated test device for the multitude of communications signal protocols in use today. An early attempt to address this problem was proposed by Harris et al. in U.S. Pat. No. 3,956,601. Harris discloses an early transmission line test device which includes a transmitter section to generate test signals, a receive section to capture test signals, and a display to report data. The Harris test device tests for various parameter conditions including envelope delay, noise, and distortion but each test modality takes place sequentially, with a selection mechanism to advance the instrument from one test to the next. A significant limitation of this approach is that only a single parameter can be tested at a time. Moreover, this early device omits the facility to test high speed optical signals, an essential component of today's telecommunication network.
A further attempt was proposed by Szymborski et al. in U.S. Pat. No. 5,121,342. Szymborski discloses a multi-mode test device which evaluates analog and digital telecommunications signals such as T1 and ISDN protocol signals but does not include the capability of processing high speed optical. signals. Szymborski utilizes a single programmable gate array to provide an interface for different transmission protocols. The line interface can be reconfigured to accommodate a different line protocol through operator input. However, the Szymborski system is limited to processing one signal at a time with its gate array devoted to one particular protocol of interest. No capability exists to test multiple lines or multiple protocols simultaneously.
Highly specialized communications line test devices have been proposed by others such as Bowmaster in U.S. Pat. No. 5,455,832 and Kight et al. in U.S. Pat. No. 5,355,238. These disclose very sophisticated communications line test devices which demonstrate the advanced nature of the SONET protocol testing art. However, neither of these advanced designs permits the exchange of signals between multiple protocols and neither permits testing of multiple protocols simultaneously. Accordingly, these disclosures contemplate the use of a dedicated line tester for each protocol under consideration.
Others have proposed commercial devices which purport to test and analyze, telecommunications lines. Companies such as Tektronix, Microwave Logic, Telecommunications Techniques Corporation, and Hewlett Packard/Cerjac have attempted to provide a test device for the telecommunications industry. Each of these devices are large, bulky test sets capable of interface with only one signal at a time. None of these devices is capable of simultaneous testing of more than one line or more than one communications protocol. Still further, none of these prior art systems provide dynamic test protocols involving multiple tests on a plurality of communications streams while maintaining the full test capability of a individual test device. As a result, qualitative comparison between different component signals in a single high bandwidth composite signal is not fully supported in prior art systems. Further, testing of multiple inbound signal protocols must be conducted sequentially, requiring a much longer test time than is desirable. For example, to test a switch which carries DS1, DS3, and SONET signals, the technician must first mate the prior art systems to the switch under evaluation and initiate a test sequence for the DS1 protocol. Upon conclusion of that test, the technician must alter the cabling of the device and initiate the DS3 test sequence. Upon the conclusion of that test, the technician must again alter the cabling of the device and initiate the SONET test sequence. This results in long test times which significantly increase maintenance and operations costs for the user.
The difficulties and limitations suggested in the preceding are not intended to be exhaustive but rather among the many which may tend to reduce the effectiveness and user satisfaction with prior communications line test devices and methods and the like. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that prior communications line test devices and methods appearing in the past will admit to worthwhile improvement.